Alarm utilizing pressure and temperature responsive switch

ABSTRACT

An electric switch in which an insulator wire and an outer conductive spring wire are wrapped about a central conductive spring wire core with the outer conductive spring wire separated at all points from the central core in its undeformed position. The three elements are normally covered by an insulator such as a tube of insulating material. The insulating winding separates the outer spring conductive wire from the central core wire in normal usage. If pressure is applied to the outer insulating covering, the outer spring conductive wire is forced into contact with the central core completing a circuit to an alarm. As soon as the pressure is removed, the spring characteristic returns the spring conductive wires to their initial position and the alarm circuit is broken. Further, the insulating winding is also temperature sensitive so that, in the case of fire, the outer spring conductive wire will make contact with the central conductive core and again close an alarm circuit.

[ Dec. 11, 1973 ALARM UTILIZING PRESSURE AND TEMPERATURE RESPONSIVESWITCH [75] Inventor: Robert W. Gould, Oakhurst, NJ.

[73] Assignee: Cable Switch Corporation, Asbury Park, NJ.

[22] Filed: Feb. 11, 1972 [21] Appl. No.: 225,461

[52] US. Cl. 340/272, 340/221 C, 200/85 R [51] Int. Cl. Htllk 3/02,G081) 13/10 [58] Field of Search 340/272, 227 C, 213,

340/258 R; 200/86 R, 86 A, 52, 61.13, 61.08

[56] References Cited UNITED STATES PATENTS 3,588,776 6/1971 Horwinski340/227 C X 3,257,530 6/1966 Davies 340/227 C 2,820,085 l/l958Crowley... 340/227 C UX 2,437,969 3/1948 Paul 200/86 R 2,790,873 4/1957Fleming 200/86 R 2,790,872 4/1957 Helsper.... 200/86 R 2,728,827 12/1955Towle 200/86 R 2,926,343 2/1960 P0stal.... 340/227 C UX 2,156,715 5/1939Basquin.... 200/86 R 3,375,477 3/1968 Kawazoe 340/227 C UX 3,052,7729/1962 Koenig 200/86 R X FOREIGN PATENTS OR APPLICATIONS 1,064,5958/1957 Germany 200/86 R 272,893 8/1928 Great Britain 200/86 R 2,013,5974/1970 France 200/86 R 390,028 3/1933 Great Britain 340/227 C PrimaryExaminer-John W. Caldwell Assistant Examiner-William M. WanniskyAttorney-Lawrence l. Lerner et al.

[57] ABSTRACT An electric switch in which an insulator wire and an outerconductive spring wire are wrapped about a central conductive springwire core with the outer conductive spring wire separated at all pointsfrom the central core in its undeformed position. The three elements arenormally covered by an insulator such as a tube of insulating material.The insulating winding separates the outer spring conductive wire fromthe central core wire in normal usage. If pressure is applied to theouter insulating covering, the outer spring conductive wire is forcedinto contact with the central core completing a circuit to an alarm. Assoon as the pressure is removed, the spring characteristic returns thespring conductive wires to their initial position and the alarm circuitis broken..Further, the insulating winding is also temperature sensitiveso that, in the case of fire, the outer spring conductive wire will makecontact with the central conductive core and again close an alarmcircuit.

7 Claims, 3 Drawing Figures ALARM UTILIZING PRESSURE AND TEMPERATURERESPONSIVE SWITCI-I BACKGROUND OF THE INVENTION There have been manyprior art pressure sensitive devices for detection of an intruder,especially those in which a wire is placed under mat. For example, U.S.Pat. No. 683,341 shows an electrical alarm mat in which an upper mesh ofwire conductors are separated from a lower mesh of wire conductor by aspring like insulation material. If one were to step above the mat, onewould force the upper wire mesh into contact with the lower wire meshand complete a circuit. If one were to lift the foot, the insulatingmaterial would return the upper wire mesh to its initial position. Thisconcept has also been shown in a strip-like form as in U.S. Pat. No.

2,728,827 which shows three parallel conductor strips separated one fromthe other by spaced insulating members and having a non-conductive tubeprotecting the entire strip. If one were to step on the strip at anypoint, one would force either the first conductor into contact with thesecond conductor or the second conductor into contact with the thirdconductor thus completing the circuit to an alarm. Here again, however,

these are flat strips and the insulating material must be.

particularly positioned along the length of the conductors.

U.S. Pat. No. 2,790,872 shows a similar pressure switch in which theinsulating member is in the form of a continuous strip wound in a spiralmanner about the central flat conducting strip. Other similar switchescan be seen in U.S. Pat. No. 2,790,873 and U.S. Pat. No. 3,052,772.

SUMMARY OF THE INVENTION The present invention relates to apressure/fire detector which is simple and easy to manufacture andinexpensive to operate and insures safe usage over long periods of time.That is, it includes a central core spring wire which is conductive, anda spirally wound insulator wound in one direction around the centralcore. A spirally wound conductor made of spring steel wire is oppositelywound around the central core and is maintained spaced from the centralcore by the spirally wound non-conductor. All three elements are placedin an insulating sleeve and, when pressure is applied, the spirallywound outer spring wire is forced between the nonconductive wiring andcomes into rubbing contact with the central core. The springcharacteristic of the spirally wound electrical outer conductor memberin cooperation with the spring characteristic of the central coremaintains a separation between the conductors until such time aspressure is again applied, e.g., someone steps on the switch. When thepressure is removed, the circuit is broken and the alarm is turned off.It should further be noted that the spirally wound nonconductor ismanufactured from a material having a low melting point so that, in caseof fire, this conductor will melt causing immediate contact between theouter spring member and the central core so that the switch acts as botha pressure detector and a fire detector. The wire is fixed at oppositeends to hold all members in place.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a switchwire constructed in accordance with the principles of the presentinvention.

FIG. 2 is a cross sectional view of the switch wire of FIG. 1 takenalong lines 22.

FIG. 3 is a schematic showing ofthe manner in which the switch wire ofFIG. 1 would be used in an alarm circuit.

In designing a switch wire for use under carpeting, mats or the like,there are many criteria which must be considered. First, the switch wiremust be sufficiently thin so as not to be noticeable, it must bemanufacturable in great lengths and flexible enough to be laid on afloor so that it gives effective coverage to the entire floor or, atleast, to those areas at which unauthorized entry might take place.Further, it must be extremely durable so that it will not wear out afterlong usage and further, must return to its normal position without failafter usage. Additionally, the switch wire must be manufacturable incontinuous lengths so that it is economical in usage in largeinstallations.

All of the above criteria are met by the present invention shown in thedrawings.

In FIG. 1, there is shown the switch wire of the present inventiongenerally designated by the numeral 10. The switch wire 10 comprises acentral spring wire conductive core 12 around which is spirally wound aninsulating member 14 which in the preferred embodiment is made of nylon.

Spirally wound in the opposite direction to the insulating winding 14 isa spring conductive member 16. The spring conductive member 16 isspirally wound with a different pitch than the spirally wound conductormember 14 and oppositely wound so that, at all points along the lengthof the switch wire 10 the spring conductive member 16 is spaced from thecentral conductor 12. The members 12, 14, and 16 are held in place bysolid terminals 24 and 26 at opposite ends thereof.

The insulating member 14 is not only electrically insulated, but can beselected to have a low melting point which allows it to act as a firedetector such as, for example, around F. The spacing between windings ofthe insulating member 14 is considerably larger than the diameter of theinsulating material. Thus, the outer spirally wound member 16 which ishelically wound over the insulator l4 and core 12 in a directionopposite to the winding direction of the insulator 14, has spacingbetween its windings which are a few times greater than the spacingbetween the insulator windings 14. The three elements 12, 14 and 16 may,depending on the specific use, be protected from environmentalcontamination by being covered with a loosely fitting tube 18.

When used in an alarm circuit, as shown in FIG. 3, the central conductor12 is connected to an alarm means such as a bell 20 in series with asource of electrical energy such as a battery 22. It is to be understoodthat the battery 22 is merely a source of electrical energy which couldbe an alternating current source and the alarm means 20 can be a light,transmitter, a remote operating alarm, or any other of the many alarmdevices presently known in the art.

When used as a pressure detector, the switch wire 10 is placed under amat, carpet, or the like. When someone steps on a given portion of themat, under which this switch wire is located, the spring steel conductor16 will, at some point along the core, make electrical contact with thecore 12. This contact will then complete the circuit to activate alarm20. Once the pressure has been removed, the outer winding 16 will, byspring action, return to its original position opening the circuit tothe alarm 20. It will be understood that the apparatus provides verylittle electrical hazzard as the system will operate on low voltages andcurrents so as to avoid any possibility of injury. The switch wire 10exhibits extremely high resistance before activation and very lowresistance upon activation. Since the invention may be used in very lowpower circuits, an insulating cover is not necessarily required. Forinstance, in an intrusion and fire alarm system it could be affixed to awooden floor with a rug placed over it. In a fire alarm system it couldbe affixed to window and door casings. If used out of doors, a weatherproof cover would be required.

Further, the switch wire 10 can be laid in any configuration to providean extended sensing area. Further, the switch wire 10 could be molded orotherwise constructed into a mat such as a welcome mat in front of anentrance way. Because of the spiral wound feature of the elements of theswitch wire 10, it can be made in indefinite lengths and can be wound onreels and then cut to length as desired. The outer jacket 18 can beplastic or other material extruded or otherwise formed around the switchwire 10. In fact, the jacket can be continuously placed on the switchwire 10 as it is being manufactured.

Because of its highly flexible nature, the switch wire 10 can be laidover irregular contours without short circuiting. Further, it can belaid around corners or in circles with radii down to about an inch. Thesensing characteristics of the switch wire 10 can be established to suitthe application, by the selection of wire sizes, insulation sizes, andwinding pitch of each of the elements 12, 14 and 16 making up the switchwire 10.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof, andaccordingly, reference should be made to the appended claims rather thanto the foregoing specification as indicating the scope of the invention.

1 claim as my invention 1. A switch wire comprising a central conductingspring core, an insulator spirally wound around said core with thespacing between adjacent windings of said insulator being greater thanthe thickness of said insulator, and a spirally wound outer springconducting member wound around said insulator and said core withouttouching said core, said outer spring member having spacing betweenwindings greater than the spacing between windings of said insulator;

said spirally wound outer spring conducting member being wound in asecond direction opposite from the direction of winding of saidinsulator.

2. The switch wire of claim 1 wherein said outer spring wire is springsteel.

3. The switch wire of claim 1 wherein said insulator is nylon.

4. The switch wire of claim 1 including a loose fitting insulatingmember extending about said core, insulator, and outer spring conductingmember.

5. The switch wire of claim 1 including a load circuit connected betweensaid core and said outer conducting spring member, said load circuitincluding a source of electric energy and a load means.

6. The switch wire of claim 5 wherein said load is an alarm means.

7. A switch wire as defined in claim 1 in which said insulator ismanufactured from a material having a low melting point.

1. A switch wire comprising a central conducting spring core, aninsulator spirally wound around said core with the spacing betweenadjacent windings of said insulator being greater than the thickness ofsaid insulator, and a spirally wound outer spring conducting memberwound around said insulator and said core without touching said core,said outer spring member having spacing between windings greater thanthe spacing between windings of said insulator; said spirally woundouter spring conducting member being wound in a second directionopposite from the direction of winding of said insulator.
 2. The switchwire of claim 1 wherein said outer spring wire is spring steel.
 3. Theswitch wire of claim 1 wherein said insulator is nylon.
 4. The switchwire of claim 1 including a loose fitting insulating member extendingabout said core, insulator, and outer spring conducting member.
 5. Theswitch wire of claim 1 including a load circuit connected between saidcore and said outer conducting spring member, said load circuitincluding a source of electric energy and a load means.
 6. The switchwire of claim 5 wherein said load is an alarm means.
 7. A switch wire asdefined in claim 1 in which said insulator is Manufactured from amaterial having a low melting point.